Hydraulic systems may include one or more valves for controlling the flow of hydraulic fluid to one or more fluid-operated devices. For example, a machine may include one or more fluid-operated actuators that may be controlled by the hydraulic system for performing work. A valve may include a cylinder and spool within the cylinder. The spool and cylinder may be configured such that movement of the spool within the cylinder opens and closes fluid passages. The opening and closing of the fluid passages may be selectively controlled to control the flow of fluid to one or more fluid-operated devices, such as, for example, hydraulic actuators.
Conventional valves may suffer from a number of drawbacks. For example, some conventional valves may suffer from slow response, which may impair an operator's use of an actuator controlled by the valve. Further, some conventional valves may suffer from a lack of resolution in response to an operator's commands, resulting in the possible impairment of an operator's ability to accurately control movement of an actuator. Another possible drawback with some conventional valves relates to inconsistent operation. For example, some conventional electro-hydraulic valves suffer from hysteresis, or the inconsistent positioning of the spool within the cylinder with respect to movement of an operator's control device. Further, the operation of some conventional valves may be adversely affected by contamination of the fluid flowing through the valve.
Thus, it may be desirable to control fluid flow in a hydraulic circuit using a valve that is more responsive to an operator's commands. Further, it may be desirable to control fluid flow in a hydraulic system using a valve that exhibits consistent operation. Moreover, it may be desirable to control fluid flow in a hydraulic system using a valve that is less sensitive to contamination.
One example of a pilot controlled valve is described in U.S. Pat. No. 4,683,915 (“the '915 patent”) issued to Sloate on Aug. 4, 1987. The '915 patent describes a pilot controlled valve having the valve body provided with a cylindrical bore and first and second radial bores on opposite sides of a land on the valve body. The valve body is slidable within an axial bore of a valve housing. The valve housing is provided with a pressure inlet port, at least one service port, and at least one pressure return port, which are axially spaced. In a central position of the valve housing, a land of the valve body isolates the pressure inlet port from the pressure return port and/or the service port, one of the radial bores is in fluid communication with the pressure inlet port, and the other radial bore is in fluid communication with either a pressure return port or service port. A rotatable control rod is positioned within the cylindrical bore of the valve body. The control rod is shaped to selectively open or close the radial bores to create a pressure imbalance across the valve body, thereby causing the valve body to shift in an axial direction.
Although the pilot controlled valve described in the '915 patent may reduce the sensitivity of the valve to contamination, the valve described in the '915 patent does not necessarily provide a valve that increases responsiveness and resolution in response to an operator's commands.
The exemplary valves disclosed herein may be directed to achieving one or more of the desires set forth above.